There’s actually a fairly good passage in the 5e DMG about making 5e more old-school. The big issues are:

* the ease with which characters regain hit-points.
* EXP for killing monsters.
* assumptions of encounter balance based on Challenge Ratings.

And that’s largely it. Use the suggested “hard core” rules for healing in the DMG, give EXP for treasures recovered (or, my personal favorite, spent), and completely ignore the CR of monsters, and you can have your old-school exploration-focused games.

As an added bonus, use Raggi’s encumbrance system from the LotFP RPG, and replace the gold standard with a silver standard. Sprinkle with Frazetta art and have at!